BUFFY SEASON 8! CONFUSION! QUESTIONS! HELP. (spoilers)

Hey guys so I just finished Lesen the season 8 of buffy and I'm so confused about.. well everything. Can someone please explain this season to me just the main stuff? I was understanding most of it but then it all just went over my head when it was revealed that Angel – Jäger der Finsternis is twilight..so was Angel – Jäger der Finsternis the bad guy? oder not? if he was then why did buffy have sex with him? didn't he kill bunch of slayers? what was that mark on the chest all about? how the hell did spike know what was going on? I'm just very very confused?? The rest of the slayers didn't lose their powers right? and did Buffy still had the superhero powers so were they destroyed when the seed was destroyed? and giles died? what? what happened to angel? what. Someone help me soon oder my brain will freaking explode. Thanks!